Chemical investigations of inorganic nanostructures

Abstract

This thesis deals with the synthesis, characterization, growth and properties of inorganic nanomaterials such as the 1D nanostructures of metal oxides and chalcogenides, and the 2D nanostructures of metal chalcogenides in the form of ultrathin filM.S.. After a brief overview of inorganic nanomaterials (Chapter 1), the results obtained on nanowires by the carbon-assisted method are described in Chapter 2. Nanowires of the oxides MgO, GeO2, and doped and undoped ITO have been prepared by the simple and versatile method. In the case of MgO, apart from nanowires the carbothermal method has been successful in yielding a variety of nanostructures which include nanotubes as well as branched and patterned nanowires. Chapter 3 describes the synthesis of nanotubes and nanowires of metal chalcogenides by a hydrogel-assisted template route. The nanostructures of the semiconducting materials- CdS, ZnS and CuS obtained by the method have been characterized by electron microscopy and optical spectroscopy. Evidence for oriented attachment of nanocrystals leading to the growth of the one-dimensional nanostructures has been observed in TEM images. The use of liquid-liquid interface for the preparation of thin filM.S. of metal sulfides and selenides has been illustrated in Chapter 4. Thus, thin filM.S. of ZnS, PbS, CdSe and CuSe have been prepared at the organic-water interface under ambient conditions. The ZnS, PbS and CuSe films. have been found to be single-crystalline by TEM analysis. In addition to the single-crystalline thin films. of metal sulfides, the method has also been used for the preparation of the bilayered film of metal sulfides- CdS-CuS. A time evolution study of the polycrystalline film of Au, CdS as well as vii single-crystalline CuS has been carried out by employing atomic force microscope. High resolution atomic force microscopy study on the effect of mechanical vibrations on the formation of Au nanoparticulate filM.S. has been presented. Besides describing features of such nanocrystalline filM.S. and their mode of formation, the interfacial rheological properties of the polycrystalline CdS film as well as single-crystalline CuS film have been examined. An important advantage of the study of materials formed at the liquid-liquid interface is that it provides a means to investigate the interface itself. In addition, it enables one to obtain substrate-free single-crystalline filM.S. of materials. In Chapter 5, the results of high-temperature synthesis of mesoporous Fm3m aluminosilicates are presented. It has been found that the synthesis temperature plays a significant role in controlling the Al content, pore volume, pore diameter, and acidity of the materials. These aluminosilicate materials have been demonstrated to show high catalytic activity in the acetylation of veratrole by acetic anhydride even at a temperature as low as 35 oC.